In U.S. Pat. No. 4,612,645, issued Sept. 16, 1986, entitled "Fast Polarization-Switchable Semiconductor Lasers" Jia-Ming Liu and Ying-Chih Chen disclose a laser device that includes a semiconductor substrate, a first cladding layer of semiconductor formed on the substrate, and an active layer of semiconductor formed on the first cladding layer for forming a junction plane between the active layer and the first cladding layer. A second cladding layer of semiconductor is formed on the active layer and a cap layer of semiconductor formed on the second cladding layer. The active layer has a lattice constant parallel to the junction plane that is sufficiently larger than the lattice constant normal to the junction plane so as to increase the optical gain of the TM mode. As a result, at a first injection current level the laser device operates in the TM mode and at a second injection current level the laser device operates in the TE mode.
In U.S. Pat. No. 4,549,300, issued Oct. 22, 1985, entitled "Semiconductor Laser Device" Mitsuhashi et al. disclose a semiconductor laser device said to effect quick switching between two polarized outputs. An antireflection coating is provided on opposite end faces and an optical system is provided for returning emitted light back into the same end face. The optical system includes an element for controlling the plane of polarization of the returned light.
In U.S. Pat. No. 4,644,553, issued Feb. 17, 1987 entitled "Semiconductor Laser with Lateral Injection" Van Ruyven et al. disclose a semiconductor device wherein an active region is bounded laterally by semiconductor regions of opposite conductivity type for laterally injecting charge carriers into an active region. The technique is said to be effective in lasers of the quantum well type.
In U.S. Pat. No. 3,301,625, issued Jan. 31, 1967, entitled "Semiconductor Light Modulators", A. Ashkin et al. disclose a light modulator wherein a depletion region of a semiconductor device is modulated for changing the characteristics of light passing through the device.
The following U.S. Patents all relate generally to laser devices. In U.S. Pat. No. 4,509,173, issued Apr. 2, 1985, entitled "Phase-Locked Semiconductor Laser Device" Umeda et al. disclose a phase-locked semiconductor laser device that is furnished locally in the vicinity of an active layer with a parallel or a meshed structure in the travelling direction of the beam. In U.S. Pat. 4,498,179, issued Feb. 5, 1985, entitled "Modulated Infrared Laser with Two Coupled Cavities" Wayne et al. disclose a gas laser having a pair of coupled laser cavities, one of the cavities being a main resonant cavity and the other including polarization coupler. In U.S. Pat. No. 4,430,740, issued Feb. 7, 1984, entitled "Long-Wavelength Semiconductor Laser" Nuyen et al. describe a number of embodiments of a semiconductor laser wherein the material constituting an active layer corresponds to the general formula: (Ga.sub.x Al.sub.1-x).sub.0.47 In.sub.0.53 As, with 0&lt;x&lt;0.27. In U.S. Pat. No. 4,207,122, issued June 10, 1980, entitled "Infra-Red Light Emissive Devices" Goodman discloses IR light emissive devices having an active region comprised of In(Sb,As) having a lattice spacing matched with GaSb.
What is not taught by this prior art, and what is thus an object of the invention to provide, is a strained-layer quantum-well semiconductor laser device having a polarization of output radiation that is switchable between the Transverse Electric (TE) and the Transverse Magnetic (TM) modes by an electric field that is externally applied perpendicularly to the layer or layers of the quantum well.
The device of Jia-Ming Liu and Ying-Chih Chen that was described previously achieves polarization switching through a change in injection current. As a result, a corresponding change in a device inversion population must also occur. However, the change in the inversion population requires some finite amount of time, thereby placing a lower limit on switching time.
It is therefore another object of the invention to provide for polarization switching through the agency of an externally applied electric field, thereby beneficially maintaining a device inversion population during the switching process to achieve extremely fast switching times.